Flocculation and specific gravity

[Rick Wise]

I'm still trying to get my arms around this concept of "flocculation and deflocculation".  Specifically, here is my question:

If I measure a glaze's specific gravity, and it is "X", and I then flocculate the glaze by adding epsom salts, will I then find that the specific gravity of the glaze has changed?  If so, will it be higher or lower?  The flocculation process makes the glaze seem "thicker" so I am assuming the SG has increased, but ...........?

[dhPotter]

The way I understand Specific Gravity, it is measuring the amount of material suspended in the water. If you take the SG prior to the "flocking" are you absolutely sure all material is suspended in the water? After "flocking", the material is suspended in the water and would give a better SG reading .

 

[Rick Wise]

But:

If we assume that it is well stirred and that consequently all materials are suspended in the water prior to the flocking, will the flocking change the SG reading?

[2Relaxed]

57 minutes ago, Rick Wise said:

But:

If we assume that it is well stirred and that consequently all materials are suspended in the water prior to the flocking, will the flocking change the SG reading?

I can't imagine why it would change as SG is simply a ratio of weight to volume. If you don't change either (assuming the amount of added Epsom salt is negligible), why would the ratio change? I'm only a newb, so anyone is welcome to disprove this!

Good (long) video: 

 

[Rick Wise]

"I can't imagine why it would change as SG is simply a ratio of weight to volume."

 

2Relaxed

Good point.  That makes sense to me

[2Relaxed]

4 minutes ago, Rick Wise said:

"I can't imagine why it would change as SG is simply a ratio of weight to volume."

 

2Relaxed

Good point.  That makes sense to me

As for what @dhPotter said, maybe it was about viscosity rather than SG?

[Hulk]

Hi Rick!

Measure your sg before and after (test an' see for yourself!)?

My guess is you'll find the sg has not changed due to your adjustment of thixotropy.

Adjusting sg and thixotropy, huuuuge breakthrough in learnin' to glaze effectively ....errr, better.

https://digitalfire.com/glossary/thixotropy

[PeterH]

@2Relaxed  I can't imagine why it would change as SG is simply a ratio of weight to volume. If you don't change either (assuming the amount of added Epsom salt is negligible), why would the ratio change? I'm only a newb, so anyone is welcome to disprove this!

Absolutely agree, with only one quibble. You need to use a reliable method of measuring the SG (as in your video). There is a long history of hydrometers providing inaccurate readings for  liquids with "difficult rheology".

The case is presented  in Why I Don’t Use a Hydrometer to Measure Specific Gravity https://suemcleodceramics.com/why-i-dont-use-a-hydrometer-to-measure-specific-gravity/, and is summarised in a quote from a 1951 pottery book: “The objections to the use of this method are many. The method is applicable only in liquids, whereas the [glaze] is not a solution but a suspension of colloids and crystalloids in a liquid; the viscous properties of the [glaze] falsify the readings of the instrument.”

PS I'm certain that there are people out there successfully using hygrometers. In which case they are probably fortunate in one way or another:
- having "magic hands"
- using "superior experimental protocol"
- choosing glazes which have sufficiently "simple rheology"

[Min]

I used to use a graduated cylinder when testing specific gravity but found using a 60 ml syringe is faster. It does hold a little back when you empty it so I draw up some water first, plunge it out then tare out the scale with the syringe on it. Then I draw up the glaze, bring it to the 50 ml  line and rinse off any glaze that gets on the outside of the syringe, weigh it then double the amount. I find it less messy than using a graduated cylinder plus it's faster. I have a few I bought super inexpensively from Aliexpress. (which should be called Alislow as it takes forever for stuff to get here)

[2Relaxed]

48 minutes ago, Min said:

 I have a few I bought super inexpensively from Aliexpress. (which should be called Alislow as it takes forever for stuff to get here)

Min, I found these also at Princess Auto in Coquitlam (they have all kinds of odd stuff there)! Sue McLeod recommended the syringe to measure SG of small test batches.

[Rick Wise]

My eyes have been opened to the benefits of flocculation!  I had thought of it only as something you do when you encounter a problem with your glaze, as opposed to a regular step in the formulation of a good glaze.  I flocculated my 3 standard glazes -- glazes that I thought were working fine -- and was amazed at the improvement.  When I compared the results it was obvious how much better the newly flocculated glazes went on and how well they covered with a nice smooth, full layer of glaze.

Would love to hear any advice about how often or under what circumstances one needs to "re-flocculate" a glaze.  What should I look for?

[PeterH]

You may find this of interest. Adjusting Glazes for Application by Pete Pinnell https://www.claytimes.com/articles/glazeadjusting.html

My reading is that you need to re-flocculate a glaze if you have deflocculated it!

In Pete's words
So why would anyone deflocculate a glaze? Well, most of the time it's not done on purpose. The alkali can dissolve out into the water from some of our materials. Yes, we try to use only insoluble materials in our glazes (i.e. materials that will not dissolve in water), but in practice some of our materials do exhibit some solubility. The amount of solubility is very small, but since the clay content in most glazes is also small (often less than 10%), even a little solubility is enough. Some of the common materials that can cause this are wood ash, soda feldspar, nepheline syenite, many common frits, and lithium carbonate. I like to think of these as our problem children: they have qualities that make us want to keep them, but they can still make our lives miserable!

[Rick Wise]

Very helpful article, thanks Peter.

[Hulk]

Hi (again) Rick!

Measure your thixotropy an' see for yourself!?

My guess is you'll find slight adjustment of thixotropy may sometimes be necessary after some time sitting in the bucket.

I'm noting each glaze's sg in my glaze notebook. After adjusting sg to a) same as last time, else b) a bit more or less, due to prior results, I'll test thixotropy by stirring clockwise (easier on my wrist, thumb, elbow, shoulder...) to match the meter of Bob Marley's "Rastaman Vibrations"; on cessation of stirring, the mass continues to revolve for just under three rotations, then comes to a stop all together, and "bounces back" a bit when it does stop. From there, tweak as necessary. Compare/contrast glaze slurry (of about same sg) that needs thixotropic adjustment - the mass continues to revolve, and obvious currents of differing speeds shear against each other; there is no mass stop, nor bounce back. Of course, you are free to choose how to match up stir rate as you wish, as well as what direction, eh? Rock on.

See Tony Hansen's video

https://www.youtube.com/watch?v=Ck_69eGJons

Ah tol' you, din' I? Hmm?

                            "Adjusting sg and thixotropy, huuuuge breakthrough in learnin' to glaze effectively ....errr, better."

[Rick Wise]

Indeed!

[Callie Beller Diesel]

The first video embedded there is by Sue Mcleod . Having read both Pete Pinnel and Tony Hansen, I have to say Sue’s in-depth explanations of glaze rheology are far better. She puts how when where and why in extensive and very easy to understand terms on her website. She also has the rare animal of a Facebook group that regularly posts accurate information and answers to questions. 
https://suemcleodceramics.com/blog/

[Mark C.]

On 11/20/2020 at 12:32 PM, Min said:

I used to use a graduated cylinder when testing specific gravity but found using a 60 ml syringe is faster. It does hold a little back when you empty it so I draw up some water first, plunge it out then tare out the scale with the syringe on it. Then I draw up the glaze, bring it to the 50 ml  line and rinse off any glaze that gets on the outside of the syringe, weigh it then double the amount. I find it less messy than using a graduated cylinder plus it's faster. I have a few I bought super inexpensively from Aliexpress. (which should be called Alislow as it takes forever for stuff to get here)

I to use the graduated cylinder but will try Mins syringe idea. The weight is far superior to the hydrometer use in terms of measurements

 

these are pretty cheap on amazon-I ordered the 100 ml ones as that what I already use in my glazes number wise

Edited November 23, 2020 by Mark C.

[Sorcery]

I have a epsom salt saturation.

20g of it weighs about 28g.

It definitely changes SG.

I don't use hygrometer, but Phil B. says they are to measure solutions, not suspensions.

I reckon they work in the same way a finger does. Repeatably. So accuracy doesn't really matter.

 

Sorce

[Min]

2 hours ago, Sorcery said:

20g of it weighs about 28g.

You lost me here.

[Rick Wise]

It threw me also the first time I read it but now I'm thinking that he is giving us a back-handed specific gravity read on it.  

[Rick Wise]

Back to my original question ("does flocculation change SG?") I'm with 2Relaxed above.  No real change.  To change SG one would have to add some mass (or weight) to the mixture (beyond the nominal weight of the epsom salt solution).

That BC mountain air must promote clear thinking.

[2Relaxed]

3 hours ago, Rick Wise said:

Back to my original question ("does flocculation change SG?") I'm with 2Relaxed above.  No real change.  To change SG one would have to add some mass (or weight) to the mixture (beyond the nominal weight of the epsom salt solution).

That BC mountain air must promote clear thinking.

Ha-ha-ha, gotta be that! Although, doesn't explain why I'm still foggy on most glaze-related topics most of the time. That was an unexpected moment of clarity. 

[Sorcery]

7 hours ago, Min said:

You lost me here.

Sorry 20ml weighs 20g.

Sorce

[Bill Kielb]

7 hours ago, Rick Wise said:

To change SG one would have to add some mass (or weight) to the mixture (beyond the nominal weight of the epsom salt solution).

Yep, the SG will change by the weight of the material you add and suspend in it. A tiny bit of epsom salt instead of water.. In other words you probably won’t be able to measure it.
Now oil, if it were 20 w 50 which floats on water because it is lighter but is very viscous ................ never mind........... viscosity and specific gravity, two very different things.

[Bill Kielb]

11 minutes ago, Sorcery said:

Sorry 20ml weighs 20g.

Hmm, yes, but probably 20 ml weighs 20.001 grams. Just likely not able to measure it.